So where did these rumors come from? It’s possible that some were deliberate hoaxes. But I decided to take a closer look at one of the most disturbing and widely disseminated bits of misinformation—the report of a fire at the Coney Island Hospital—and found that it originated not as a prank, but as a report on a police scanner. Typically the province of local news reporters and hobbyists, the scanner became a widely relied-upon resource last night thanks to an online audio player that allowed people to tune in even if they didn’t have an actual radio.

From there, it was spread far and wide by Twitter users who apparently viewed the scanner as a solid primary source.

But as any local news reporter knows, the scanner is not a solid primary source. It’s a forum through which police and firefighters communicate and trade tips with dispatchers, sifting through information that often comes second- or third-hand, through residents’$2 911 calls and witnesses in the field. As these tips come in, officials are sent out to investigate them. Only once they’re on scene can they begin to determine whether the reports are true. And in fact, that’s exactly what happened with the hospital fire.

Thankfully, as much as Twitter can be a font of falsehoods, it is typically almost as quick to home in on the truth. In this case, it was a local news blog, Sheepshead Bites, that sussed out what appeared to be the origin of the Coney Island rumors (though it’s worth noting that this report, too, was third-hand). Its debunking quickly made the rounds.

Buzzfeed’s John Herrman this morning praised Twitter as a truth machine. But that’s only half the story. Certainly the site helped truth-seekers get to the bottom of a number of myths. On the other hand, without Twitter, many of those myths would never have spread so far in the first place. And some, it seems, live on…